Department of Quantum Materials

Entanglement of electrons (electron correlations) in solids, in combination with details of the crystal lattice structure, produce a surprisingly rich variety of electronic phases, that are liquid, liquid-crystal and crystalline states of the charge and spin degrees of freedom. These complex electronic phases and the subtle competition among them very often give rise to novel functionality. The department will be studying these interesting novel phases in transition metal oxides and related compounds where the narrow d-bands, which give rise to strong electron correlations, in combination with the rich chemistry of such materials provides excellent opportunities for new discoveries. The goal of this research will be to hunt for new materials exhibiting exotic electronic states of matter, showing phenomena such as superconductivity or high thermoelectricity, and to explore them with advanced measurement techniques to unveil the physical mechanisms that could be drivers of potentially highly desirable functionality.


Diamagnetism was first discovered in 1778 by Anton Brugmans in elemental Bi. In retrospect, his observation was likely enabled by the large diamagnetism of Bi compared with conventional diamagnetic insulators. Many years later, the origin of the giant diamagnetism in Bi emerged a big puzzle in condensed matter physics. After decades of debate, the effect was theoretically understood to arise from the orbital magnetism of Dirac electrons via inter-band mixing, and recent reports of large diamagnetism in the bulk magnetic susceptibility of several Dirac semimetals have been similarly interpreted. To our surprise, however, no direct experimental evidence for the giant orbital diamagnetism of Dirac electrons has been provided so far even in Bi, as it is nontrivial to experimentally identify the “orbital contribution” of “Dirac electrons” in the magnetic response.
Our work on the three-dimensional Dirac electron system Sr3PbO provides for the first time an experimental proof that the giant diamagnetism indeed originates from the orbital magnetism of Dirac electrons, based on a very careful analysis of the NMR Knight shift and the spin relaxation rate together with the bulk magnetic susceptibility. more

was awarded the Eugen and Ilse Seibold Prize of the German Research Foundation. This prize is awarded to Japanese and German researchers in recognition of their exceptional contribution towards advancing understanding between the two countries.
An international team of scientists from Max Planck Institute for Solid State Research, University of Stuttgart, and University of Tokyo has experimentally observed an exotic quantum state of matter: a spin-orbital-entangled quantum liquid formed by iridium magnetic moments on a honeycomb lattice in the compound H3LiIr2O6. The iridium moments do not exhibit any type of magnetic ordering and remain quantum disordered down to very low temperatures compared to the strength of their pairwise interactions. Instead, the iridium moments liquefy into a highly-entangled, quantum, spin-liquid state involving not only spins but also orbital moments of iridium electrons. more
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